The sense of feel is not typically used as a man-machine communication channel, however, it is as acute and in some instances as important as the senses of sight and sound, and can be intuitively interpreted (e.g., think of one's response to being tapped on the shoulder). Using an intuitive body-referenced organization of vibrotactile stimuli, information can be communicated to a user. Military/industrial applications include improved situation awareness to operators of high performance equipment and weapon platforms. Consumer applications include conveying tactile information from a video game and supplementing audio/visual output with tactile sensations related to movies and music.
Tactile stimuli provides a silent and invisible, yet reliable and easily interpreted communication channel, using the human's sense of touch. A single vibrotactile transducer can be used for a simple application such as an alert. A plurality of vibrotactile transducers can be used to provide more detailed information, such as spatial orientation of the person relative to some external reference. Such vibrotactile displays have been shown to reduce perceived workload by its ease in interpretation and intuitive nature. Broadly, this field is also known as haptics.
The key to successful implementation of a vibrotactile transducer for the applications described above lies in the ability to convey a strong, localized vibrotactile sensation to the body with compact, lightweight devices that can be held against the user's body without impairing movement or causing discomfort. As such, they should be thin and lightweight, and should be suitable for incorporation in or under clothing. These devices should be electrically and mechanically safe and reliable in harsh environments, and drive circuitry should be compatible with standard digital communication protocols to allow simple interfacing with a controller such as a computer or other digital control system.
Various types of vibrotactile transducers, suitable for providing a tactile stimulus to the body of a user, have been produced in the past. Prior vibrotactile transducers designs have incorporated electromagnetic devices based on a voice coil (loudspeaker or shaker) design, an electrical solenoid design, or a simple variable reluctance design. The most common approach is the use of a small motor with an eccentric mass rotating on the shaft, such as shown in U.S. Pat. No. 3,361,130 and as used in pagers and cellular phones. When implemented as small, wearable devices, these transducers produce only a low level vibrational output, making them difficult to be perceived by a user who is not concentrating on trying to detect the sensation. They also, in general, provide a diffuse type sensation, so that the exact location of the stimulus on the body may be difficult to discern; as such, they might be adequate to provide a simple alert such as to indicate an incoming call on a cellular phone, but would not be adequate to provide spatial information by means of the user detecting variable stimuli from various sites on the body. Typically these devices operate at a single frequency, and cannot be optimized for operating over the frequency range where the skin of the human body is most sensitive to vibrational stimuli. Rotating devices have a particular problem with start up, since they have to rotate up to speed, so there is a delay between activating the device and the vibrational output.
Piezoelectric designs have also been used for vibrotactile transducers, but in general provide very small displacements, resulting in low vibration output unless the device is very large. Devices such as the Optacon, a reading machine for the blind, use an array of piezoceramic bimorph benders to activate a matrix of rods held against the user's fingertip (Linvill, J. G., EEE Trans on Audio and Electro., Vol. AU-17, No. 4, 271-274, 1969.). Again, the tactile stimulus is relatively low, making it only useful on areas of the body that have a low threshold of vibrotactile detection, such as the fingertips. Other piezoceramic approaches have used benders to impart a lateral motion against the skin, but they tend to be easily damped when in contact with the skin, thus reducing their motion and consequently, their detectability.
More recent applications of vibrotactile stimulus have been related to entertainment applications, such as providing vibrational stimulus to reinforce the sound and graphics for video games and theme park rides. These applications use techniques such as blowing a jet of air against the skin, vibrating the entire seat or floor using a subwoofer or shaker type device (such as in Clamme U.S. Pat. No. 5,973,422 and Bluen et al. U.S. Pat. No. 5,424,592), or using other mechanically actuated devices such as electrical solenoids that contact the body through an opening in a seat. While these devices can provide high levels of sensation, they do not meet the requirement addressed by this invention, in that they are large, require high power, and are typically directly mounted to seating or a floor.
The study of mechanical and/or vibrational stimuli on the human skin has been ongoing for many years. Schumacher et al. U.S. Pat. No. 5,195,532 describes a diagnostic device for producing and monitoring mechanical stimulation against the skin using a moving mass contactor termed a “tappet” (plunger mechanical stimulator). A bearing and shaft is used to link and guide the tappet to the skin and means is provided for linear drive by an electromagnetic motor circuit, similar to that used in a moving coil loudspeaker. The housing of the device is large and mounted to a rigid stand and support, and only the tappet makes contact with the skin. The reaction force from the motion of the tappet is applied to a massive object such as the housing and the mounting arrangement. Although this device does have the potential to measure a human subject's reaction to vibratory stimulus on the skin, and control the velocity, displacement and extension of the tappet by measurement of acceleration, the device was developed for laboratory experiments and was not intended to provide information to a user by means of vibrational stimuli nor be implemented as a wearable device.
Electromagnetic transducers such as used in U.S. Pat. No. 5,195,532 are effective mechanisms to produce the required oscillatory motion for a vibrotactile transducer, but are typically large and inefficient. U.S. Pat. Nos. 5,973,422 and 5,424,592 disclose improved configurations of electromagnetic transducers for use as a low-frequency vibrator/shaker. The electromagnetic moving mass transducer configuration described by U.S. Pat. No. 5,973,422 is based on well known mass-spring, force actuator systems, where the ratio of “reciprocating member” or moving mass and the magnet spring constant should be chosen to achieve substantially the square of the radian resonance frequency. This model holds true if the mass of the housing is assumed to be large (relative to the moving mass) and rigid (free of mechanical resonance frequencies). It further neglects the effect of any mechanical load on the reciprocating member, and assumes that there is negligible damping (resistance) applied to the reciprocating member.
U.S. Pat. Nos. 5,973,422 and 5,424,592 thus present shaker or vibrator configurations that provide high force, work well at low frequencies, typically less than 100 Hz, and have minimal or no loading on the reciprocating member (moving mass). As implemented, the transducer in U.S. Pat. No. 5,424,592 is 3 lb. with a 40 Hz resonance, and the transducer in U.S. Pat. No. 5,973,422 is implemented as an 11 lb. device. Both devices are practically implemented as having their housing attached to a massive object (e.g., furniture, floor) and the moving mass is not in direct contact with the a load.
In summary, the prior art describes large, massive, high output force and displacement devices configured as “bass shakers” typically applied to audio-visual applications, and small, low output displacement devices capable of providing only a weak stimulus to the skin of a user. The prior art fails to recognize the design requirements to achieve a small, wearable vibrotactile device that provides strong, efficient vibration performance (displacement, frequency, force) when mounted against the skin load of a human. This is particularly true when considering the requirement to be effective as a lightweight, wearable tactile display (e.g., multiple vibrotactile devices arranged on the body) in a high noise/vibration environment as may be found, for example, in a military helicopter. It is not possible to simply scale the mechanical design configurations of high displacement/force prior art transducers, such as moving mass mechanical actuators, to a frequency range or physical size applicable to wearable tactile vibrator systems since, in a practical, wearable implementation, the mass of the housing will be small, and both the moving member and the housing will be in contact with the skin, violating the design criteria presented for these designs. To achieve a lightweight vibrotactile transducer that is capable of the required vibration level for tactile awareness, the complex-valued mechanical impedance of the load (in this case, the human skin) must be considered and a more complete description of the transducer system must be used. Further, and most importantly, the complex-valued mechanical impedance of the skin load and the required vibration level for tactile awareness determine the optimal selection of housing or stator mass, movable mass and the spring rate of the suspension spring.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.
The present invention provides a novel implementation of a dual-moving mass transducer with a physical configuration and design selected for maximum effectiveness in meeting the requirement for a high output displacement, wearable vibrotactile transducer. The term dual moving mass is used herein to denote the fact that the transducer housing is designed to vibrate at a reduced level and substantially out of phase with the moving member (skin contactor) when both the housing face and contactor face are in simultaneous contact with the skin load, making the device practical as a wearable, vibrational transducer, and distinguishing it from prior art designs that fail to address a housing that is lightweight and not attached to a rigid base.